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Vulnerable Software

Vulnerability Details CVE-2026-81725

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.002
EPSS Ranking 12.6%
CVSS Severity
CVSS v3 Score 3.7
Products affected by CVE-2026-81725
  • Nltk » Nltk » Version: 2.0.1
    cpe:2.3:a:nltk:nltk:2.0.1
  • Nltk » Nltk » Version: 2.0.3
    cpe:2.3:a:nltk:nltk:2.0.3
  • Nltk » Nltk » Version: 2.0.4
    cpe:2.3:a:nltk:nltk:2.0.4
  • Nltk » Nltk » Version: 3.0.0
    cpe:2.3:a:nltk:nltk:3.0.0
  • Nltk » Nltk » Version: 3.0.1
    cpe:2.3:a:nltk:nltk:3.0.1
  • Nltk » Nltk » Version: 3.0.2
    cpe:2.3:a:nltk:nltk:3.0.2
  • Nltk » Nltk » Version: 3.0.3
    cpe:2.3:a:nltk:nltk:3.0.3
  • Nltk » Nltk » Version: 3.0.4
    cpe:2.3:a:nltk:nltk:3.0.4
  • Nltk » Nltk » Version: 3.0.5
    cpe:2.3:a:nltk:nltk:3.0.5
  • Nltk » Nltk » Version: 3.1
    cpe:2.3:a:nltk:nltk:3.1
  • Nltk » Nltk » Version: 3.10.0
    cpe:2.3:a:nltk:nltk:3.10.0
  • Nltk » Nltk » Version: 3.10.1
    cpe:2.3:a:nltk:nltk:3.10.1
  • Nltk » Nltk » Version: 3.10.2
    cpe:2.3:a:nltk:nltk:3.10.2
  • Nltk » Nltk » Version: 3.2
    cpe:2.3:a:nltk:nltk:3.2
  • Nltk » Nltk » Version: 3.2.1
    cpe:2.3:a:nltk:nltk:3.2.1
  • Nltk » Nltk » Version: 3.2.2
    cpe:2.3:a:nltk:nltk:3.2.2
  • Nltk » Nltk » Version: 3.2.3
    cpe:2.3:a:nltk:nltk:3.2.3
  • Nltk » Nltk » Version: 3.2.4
    cpe:2.3:a:nltk:nltk:3.2.4
  • Nltk » Nltk » Version: 3.2.5
    cpe:2.3:a:nltk:nltk:3.2.5
  • Nltk » Nltk » Version: 3.3
    cpe:2.3:a:nltk:nltk:3.3
  • Nltk » Nltk » Version: 3.4
    cpe:2.3:a:nltk:nltk:3.4
  • Nltk » Nltk » Version: 3.4.1
    cpe:2.3:a:nltk:nltk:3.4.1
  • Nltk » Nltk » Version: 3.4.3
    cpe:2.3:a:nltk:nltk:3.4.3
  • Nltk » Nltk » Version: 3.4.4
    cpe:2.3:a:nltk:nltk:3.4.4
  • Nltk » Nltk » Version: 3.4.5
    cpe:2.3:a:nltk:nltk:3.4.5
  • Nltk » Nltk » Version: 3.5
    cpe:2.3:a:nltk:nltk:3.5
  • Nltk » Nltk » Version: 3.6
    cpe:2.3:a:nltk:nltk:3.6
  • Nltk » Nltk » Version: 3.6.1
    cpe:2.3:a:nltk:nltk:3.6.1
  • Nltk » Nltk » Version: 3.6.2
    cpe:2.3:a:nltk:nltk:3.6.2
  • Nltk » Nltk » Version: 3.6.3
    cpe:2.3:a:nltk:nltk:3.6.3
  • Nltk » Nltk » Version: 3.6.4
    cpe:2.3:a:nltk:nltk:3.6.4
  • Nltk » Nltk » Version: 3.6.5
    cpe:2.3:a:nltk:nltk:3.6.5
  • Nltk » Nltk » Version: 3.6.6
    cpe:2.3:a:nltk:nltk:3.6.6
  • Nltk » Nltk » Version: 3.6.7
    cpe:2.3:a:nltk:nltk:3.6.7
  • Nltk » Nltk » Version: 3.7
    cpe:2.3:a:nltk:nltk:3.7
  • Nltk » Nltk » Version: 3.8
    cpe:2.3:a:nltk:nltk:3.8
  • Nltk » Nltk » Version: 3.8.1
    cpe:2.3:a:nltk:nltk:3.8.1
  • Nltk » Nltk » Version: 3.9
    cpe:2.3:a:nltk:nltk:3.9
  • Nltk » Nltk » Version: 3.9.1
    cpe:2.3:a:nltk:nltk:3.9.1
  • Nltk » Nltk » Version: 3.9.2
    cpe:2.3:a:nltk:nltk:3.9.2
  • Nltk » Nltk » Version: 3.9.3
    cpe:2.3:a:nltk:nltk:3.9.3
  • Nltk » Nltk » Version: 3.9.4
    cpe:2.3:a:nltk:nltk:3.9.4


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